Mine sure does, but I found a simple solution that keeps things cool without a lot of whoosh noise.

I have a CSi/SPECO 13.8 Volt 18 Amp model which serves my puny little 100 Watt station very well.

This power supply is a linear regulated type with plenty of pass transistors in the back embedded in a nice large heatsink. There are two problems: the heatsink fins are oriented horizontally and the heatsink gets far too hot to touch after being on for a while.

I know… I know many of you are thinking my 18 amp power supply is a little underrated for a 100 Watt station and that is the reason for the excessive heat. You may have a point, but the situation here is this power supply gets way too hot to touch with no load on it. It takes quite a while, but the heat eventually builds up and reaches an equilibrium point where you simply cannot touch it for more than a few seconds. I never measured the temperature so cannot be sure how hot it really got. It was just… hot.

As a circuit designer I am well aware of how much punishment good final transistors can take (some have max junction temperatures of 275 C!!!). However, cooler running is always going to increase reliability of all electrical components.

It’s a shame the heatsink is oriented horizontally as the system would probably be measurably cooler with chimney effect air flow. I was not willing to put the power supply on its side.

So what to do…

Adding a fan to move air across the heatsink was an obvious necessity. I considered AC fans and 12 Volt fans, but found them to be quite loud. They work fine, but made far too much whoosh noise. They work so well they blow a great deal of air across the heatsink, but I wondered if I really needed so much air flow to get my high temperature under control.

As it turns out I had a similar issue back in the 1990s when faced with defending the movement of a heatsinked 7905 regulator connected to -12 Vdc from just above some cooling fans to a few inches away. The original designers were concerned my moving the regulator away from the direct blast of the fans would be too costly in cooling performance.

The regulator was dissipating several watts of power so this was a reasonable question. I devised a test to determine the cooling performance of air flowing past a heat sink vs. the fan-heatsink distance.

I moved the regulator circuit with its heatsink out of the cooling cage and into still air. I placed a thermocouple on the heatsink. I obtained a muffin fan and wired it up to a power source. While holding the fan various distances from the regulator, I made the following observations.

Fan Off:

The temperature of the heatsink climbed steadily past 50 degrees C above ambient reaching dangerous levels in a short time terminating this test.

Fan On and held 1 inch from the heatsink:

The temperature of the heatsink remained at room temperature.

Fan On and held 6 inches from the heatsink:

The temperature of the heatsink was, maybe, about 1/2 degree above ambient.

Fan On and held 12 inches from the heatsink:

The temperature was about 2 degrees above ambient.

Fan On and held 18 inches from the heatsink:

The temperature was about 4 degrees above ambient.

Fan On and held 24 inches from the heatsink:

The temperature was about 7 degrees above ambient… O come on how can this be still cooling the regulator at two feet?

Fan On and held 32 inches from the heatsink:

Temperature about 20 degrees above ambient.

Fan On and held about 36 inches form the heatsink:

Temperature about 40 degrees above ambient and varying quite a bit.

This data is better shown in the graph below…

Heat Rise vs. Fan Distance (Airflow)

This revealing test shows fin heatsinks are actually very good at coupling heat to the air with remarkably little airflow. However, there has to be at least some airflow to prevent heat saturation at the heatsink air boundary and that is, apparently, where you realize most of the cooling benefit.

All I needed was some airflow, not a hurricane.

All the fans I found all worked great, but made a lot of noise. I thought about creating a simple little regulator circuit to knock down the 13.8 Vdc to something lower and slower. With the goal of operating a fan lower than its voltage rating I remembered some DC busses run at 24 volts or so and have plenty of compatible products including fans.

So I decided to purchase a 24 Vdc fan and run it off the 13.8 Vdc power supply voltage to slow it down to a slight breeze. Avoiding the step down regulator by simple component choice kept things straightforward.

Here is the simple install of my 24 volt fan running “slow.”

Slow running fan provides adequate air flow.

The use of banana plugs keeps fan power connections tidy.

I found some twisted pair cable and used that to connect the 24 Vdc fan to the power supply’s output via a couple of banana plugs. The green banana plug is not related to the fan, but illustrates the ease of adding more connections by stacking the banana plugs. No RigRunners or Anderson Power Poles needed for this low current load.

Results?

With the 24 volt fan running on 13.8 Vdc, it quietly and gently provides airflow across the horizontal fins of the power supply’s heatsink. This airflow works so well you can barely feel any rise in temperature when touching the heatsink. Success!

The final issue I had with this arrangement was the fan vibrating my desktop thereby generating audible noise. This was easily solved by putting a loosely folded piece of paper underneath the fan to serve as a vibration isolator. It works FB. No its not earthquake proof, but functional.

Conclusion

Power supplies, especially economy models like mine, often omit fans and rely on the very high temperature rated components to just take the abuse. This can work, but the addition of a simple 24 Vdc fan running slow on the supply’s 13.8 Vdc output provides more than enough cooling capacity to keep the output transistors at a far lower temperature than without. Cheaper insurance is hard to find.

Cool your power supply today… It will love you for it.

If you are using generators at your Field Day please have a look at these posts for some previous lessons learned…

The Honda Inverter generators are, by far, the most fantastic generators ever to hit the market. Even with that fuel cap issue, they are still worth it. So very quite and such clean power… nice.

GL

If you are thinking of participating in your local club’s Field Day festivities or are heading to the campground with your family for a Bravo station, bonus points are available.

One of my favorites is the Alternate Power Field Day bonus.

To quote the ARRL Field Day rules for 2009…

“7.3.8. Alternate Power: 100 bonus points for Field Day groups making a minimum of five QSOs without using power from commercial mains or petroleum driven generator. This means an “alternate” energy source of power, such as solar, wind, methane or water. This includes batteries charged by natural means (not dry cells). The natural power transmitter counts as an additional transmitter. If you do not wish to increase your operating category, you should take one of your other transmitters off the air while the natural power transmitter is in operation. A separate list of natural power QSOs should be submitted with your entry. Available to Classes A, B, E, and F.”

Last year one of our club members brought a fold out solar panel array. Originally he hooked it up to a FM HT. The solar panels powered the HT just fine, but no one was on the air to make contact with.

Then an Elecraft K1 transceiver arrived. Hmmm…

Since the K1 is an HF transceiver one of the other stations (we were 4A last year) would have to cease operation while we operated the solar powered station.

No problem. We went to our CW tent and…

• Disconnected the antenna coax from the main CW transceiver (a Yeasu FT-2000 by the way – nice)
• Connected the antenna coax to the K1
• Flipped the solar panels out along the ground
• Hooked up the power to the K1
• One person operated the key and the K1
• While the person in the CW tent logged the QSOs on the N3FJP Network software
• and made note of these particular QSOs as “Alternate Power” contacts
• Logged five Alternate Power QSOs
• Reversed the process to get the CW Station back the way it was and continue to operate normally
• Done!

Here is our K1 operator, logger (in the tent) and the impressive solar array…

Making Solar Power QSOs during Field Day

This was pretty easy really.

In this case, the low current draw of the Elecraft K1 really helped. We did not need any temporary storage from a battery in parallel with the solar output. It all just worked straight off the solar power source. Nice.

You may desire to try the above and I really do suggest it. It is fun. If your rig needs a bit more power than the K1, consider adding the battery and letting it charge for a bit before making those five QSOs.

I hope to hear all of you on Field Day. Good Luck.

Of course the buzz word of the decade when talking about batteries is Lithium, Lithium, Lithium.

Sure enough batteries based on Lithium chemistry yield energy densities exceeding 100 Wh/kg and quite often much higher. That’s great. However, let’s compare it with a typical gel cell type lead acid battery.

My example battery is a Yuasa NP7-12. Complete specs include:

• Make: Yuasa
• Model: NP7-12
• Voltage: 12V
• Amp-Hours: 7 AH
• Calculated Watt Hours: 84 Whrs

I weighed the battery and it came to about 6 pounds or 2.7 kilo-grams.

Thus, the energy density is about…

This is less than one third the capacity of most Lithium battery types.

On the other hand, it is not that radiacally different and the good old Gel Cell is a battery type very well understood by a great many folks.

Weight matters in my application because I have to carry this power source up a few thousand feet of steep trails to reach the White Rock Cliff Station 6 of the Appalachian Trail Golden Packet (ATGP) attempt.

A 7 AH battery is probably good enough for the Kenwood D710 in this particular project, but I am not yet convinced this is true. Calculations for the energy needed for the ATGP is for a future post. Stay tuned.

If I can trade battery weight for water supply I think I will be much happier.

John

This situation is quite likely very common among amateur radio operators who keep a simple shack set up with one large power supply feeding multiple loads.

Many operators use a DC power distribution system like the RIGrunner from West Mountain Radio to distribute the power.

In this case, the viewer simply has the power cords for both radios tied straight to the DC power output posts on the power supply.

Equipment involved includes:

• Power Supply Astron RS35A
• IC-746 (the non pro version)
• Kenwood TS-180S

The problem:
Whenever the Kenwood TS-180S radio is powered on, the Icom IC-746 will not transmit and the display screen goes white with no visible characters.

If you turn the Kenwood TS-180S off, the Icom-746 returns to normal operation.

The Kenwood radio shows no problems when the Icom is on or off.

The viewer asks for thoughts on what may be causing this behavior.

We used this UPS to power the computer running as logging server for the N3FJP software as well as the Linksys WRT54G router.